Advances in biology have laid the basis for molecular medicine - the identification and correction of molecular errors that underlie disease. This, coupled with rapidly evolving innovations in imaging and computing technology, is driving a revolution in a field referred to as "molecular imaging", i.e., imaging that provides non-invasive visualization of molecular distribution and function in living systems ranging from individual cells to human beings. Indeed, it is expected that molecular imaging will become the primary mechanism by which new treatments are translated into clinical use and optimized for individual patients. With support from an NIH/NCI P20 planning grant, a molecular imaging center is currently being developed on the Health Sciences campus of the University of Southern California (USC) as a joint effort between the USC PET Imaging Science Center (PET ISC) and the Norris Comprehensive Cancer Center (NCCC). This has given rise to a number of collaborative projects between investigators in the PET ISC and biologists at the Cancer Center. The equipment requested in this proposal will be used primarily to support the collaborative effort between the PET ISC and NCCC. The USC School of Medicine recently financed renovations that provide an Imaging Laboratory within the PET ISC adjacent to our cyclotron/radiochemistry facility. The Imaging Laboratory is currently equipped with an autoradiography system, a full-scale PET scanner for large animals and a new miniature PET scanner for rodents. This proposal requests funding to equip the PET Imaging Laboratory for optical Imaging at the microscopic and small-animal levels. This will greatly enhance the effectiveness of our experimental radionuclear imaging capabilities by permitting (a) complementary visualization of gene expression and protein function at the cellular, tissue and whole-animal levels, and (b) efficient and accurate preparation of tumor-bearing and transgenic mice and rats. Optical Imaging is easier and cheaper, while radionuclear techniques provide accurate absolute quantitation in 3 dimensions. PET techniques developed in preclinical studies with the support of optical imaging should translate more or less directly into clinical applications.